1. Field of the Invention
The invention relates to a diaphragm for use in a switch employing a dome-shaped switch for various electronic apparatuses, and a method for manufacturing the same. In addition, the invention relates to a membrane switch and an input device employing the above diaphragm for use in a switch.
2. Description of the Related Art
Dome-shaped switches are used in various electronic apparatuses. Such switches include, as shown in FIG. 1A, a contact member (hereinafter, referred to as “diaphragm”) 103 made of a conductive material and which is disposed on a wiring board 100 having a C-shaped first electrode 101 and a second electrode 102 located at the center portion of the first electrode 101 and spaced apart therefrom. Via the diaphragm 103, an electric contact is established between the first electrode 101 and the second electrode 102, which are insulated from each other, which turns the switch on. A part of a lead portion extending from the second electrode 102 is covered with an insulating sheet 104 so that the lead portion is insulated from the diaphragm 103.
As shown in FIG. 1B, the diaphragm 103 is disposed above the wiring board 100 so that the periphery of the diaphragm 103 comes in contact with the C-shaped first electrode 101.
As shown in FIG. 1C, when the center portion of the diaphragm 103 in which the periphery thereof comes in contact with the first electrode 101 is depressed, the center portion of the diaphragm 103 comes in contact with the second electrode 102. As a result, an electric contact is established between the first electrode 101 and the second electrode 102 via the diaphragm 103, which turns the switch on.
In the related art technique, a round dome-shaped diaphragm for use in a switch (switch diaphragm), such as the one shown in FIGS. 2A and 2B, is used, and a switch is constructed so that the electric connection between the first and the second electrodes 101 and 102 is controlled via the diaphragm 103.
The round dome-shaped switch diaphragm 103 includes a convex curved portion and a base portion provided therearound (see FIG. 2A). When the center portion of the switch diaphragm 103 is depressed, a portion extending between the convex curved portion and the base portion is deformed (see FIG. 2B). As a result, the center portion of the diaphragm 103, the periphery (base portion) of which comes in contact with the first electrode, comes in contact with the second electrode 102 (see, for example, Japanese Patent Application, First Publication No. 2004-31154).
Furthermore, recently, the reduction in the sizes of electronic apparatuses has resulted in a reduction in the sizes of various switches. Consequently, a reduction in the diameter of round dome-shaped diaphragms used in dome-shaped switches is desired. However, a small-diameter diaphragm has a short operating stroke, which does not provide a satisfactory “click feeling” to users. To address this issue, a new approach has been proposed in which a round dome-shaped diaphragm having a larger curvature is used to extend the operating stroke, for example. However, a larger load is required to click a round dome-shaped diaphragm having a large curvature, which may impair the “click feeling.”